This has been going on for a while now: a set of files that was already in the library will be marked as newly "added". Then, while MM4 is open, those files disappear. After a complete manual rescan, those files re-appear - only to disappear again once I close and start MM4 again (I have continuous scans and scans at startup active).

I have already deactivated my file sync tool (syncthing), which I initially thought to be responsible. Also, some files have special characters in their properties and filename, but not all. Moreover, sometimes this appears to affect random files - single files from an album will suddenly be duplicated, and then be reported missing.

It's a big mess, and I don't know what's going on. Is my database corrupt?